Design and Hysteresis Modeling of a Miniaturized Elastomer-Based Clutched Torque Sensor

Abstract

Elastic torque sensors have been widely used for small-scale robots such as hand exoskeletons to achieve torque control. However, designing a miniaturized and lightweight elastic torque sensor with human–machine interaction safety is still a challenge. In this article, a novel miniaturized and lightweight elastomer-based clutched torque sensor is presented. A rubber spring is designed and used to reduce its volume and weight. A wafer disk clutch is devised to improve mechanical safety. The torque sensor is 29.5 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times18$ </tex-math></inline-formula> mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times24$ </tex-math></inline-formula> mm in dimension and weighs 23 g. Compared with the state-of-the-art elastic torque sensors for hand exoskeletons, the volume-to-torque ratio is reduced by 15.48%, and its weight is reduced by 23.33%. Since the hysteresis characteristics of the rubber spring leads to a nonlinear deformation–torque relationship, an improved parametric Gaussian process regression (PGPR) method based on the nonlinear autoregressive moving average structure with exogenous inputs (NARMAX) is proposed. A combined kernel function for the improved PGPR is designed to improve the fitting performance. Finally, experiments have been conducted to verify the mechanical safety and torque sensing performance. The force caused by collision on the proposed torque sensor is less than that on the torque sensor without the clutch (reduced by 51.78%). The proposed hysteresis model can reduce the maximum absolute modeling error to 7% compared with those of other intelligent hysteresis models (the modeling error is 12.32%). Therefore, the experimental results indicate that the proposed torque sensor can improve the mechanical safety and achieve accurate torque sensing.